I've had it activate a few times when I'm "driving like I stole it".
One scenario, on a dual carriageway, car in front was turning left. I was approaching, shall we say "quite rapidly", and was about to over take into the right hand lane. But the NX deemed it too close for comfort, slowed the car down quite abruptly, BEEP BEEP BEEP from the dash, and BRAKE!!! written on the dash.
At no point do I think I was even going to come close to rear ending the car in front.